Aminoglycosides are among the most commonly used broad-spectrum antibiotics. They are often used in combination with other antibiotics, such as β-lactams, as the first line of defense against serious infections caused particularly by various gram-negative bacteria (Wrght et al., 1998; Coates et al., 2002; Vakulenko and Mobashery, 2003). Structurally, aminoglycosides most often comprise a central 2-deoxystreptamine aminocyclitol ring to which amino sugars are linked by means of α-glycosidic bonds either at positions 4 and 5 (e.g. neomycin B) or at positions 4 and 6 (e.g. gentamicin C1) (FIG. 1).
At physiological pH, the amino groups of aminoglycosides are protonated to yield polycations that bind to the major groove of polyanionic 16S rRNA (on the 30S ribosome) of prokaryotic cells (Recht et al., 1999; Fourmy et al., 1997; Fourmy et al., 1998), thereby impeding the synthesis of bacterial proteins. The high level of affinity between aminoglycosides and RNA is more likely the result of nonspecific electrostatic interactions (Wang and tor, 1997; Roestamadji et al., 1995), whereas the specificity of aminoglycosides is believed to be determined by hydrogen bonding between the RNA and the upper two rings of the aminoglycosides (Vicens and Westhof, 2003; Ryu et al., 2002).
Recently, increasing evidence has suggested that RNA may become a prime target for antiviral therapy (gallego and Varani, 2001; Hermann, 2000), as supported by a growing interest for small molecules capable of interfering with RNA. Among these small molecules, aminoglycosides are arguably the most studied and best characterized. Aminoglycosides have become leading structures for studying RNA-ligand interactions as well as for designing novel ligands for nucleotides (Tok et al., 2003; Seeberger et al., 2003). Many aminoglycoside derivatives have shown antiviral activity by binding to specific regions of viral RNA (Luedtke et al., 2003; Arya et al., 2004; Liu et al., 2004; Litovchick et al., 2000).
One of the many features of aminoglycosides resides in their ability to recognize secondary and tertiary structures of RNA in which the base pairing has been disrupted (e.g. bulges, internal loops and stem junctions). A specific example of such secondary and tertiary structures constitutes the bulge regions of unrelated RNA sequences from the 16S ribosome, HIV TAR, HIV RRE, and the Group I intron (Wang et al., 1997; Arya et al., 2001; Arya et al., 2001). Furthermore, aminoglycosides specifically bind to kissing-loop complexes formed by the RNA dimerization initiation site of the HIV virus (Russell et al., 2003), stabilize DNA-RNA triplexes and hybrid duplexes, and even induce hybrid triplex formation (Sucheck et al., 2000; Arya et al., 2003). The use of aminoglycosides as antiviral agents has been previously suggested.
The rapid emergence of bacterial resistance to aminoglycoside antibiotics is severely limiting their use and mitigating clinical efficacy in severe bacterial infections, thus creating a pressing need for the discovery and development of structurally novel and more potent antibiotics (Walsh, 2003). One alternative to circumvent bacterial resistance is through derivatization of existing antibiotics (Tok et al., 2003; Seeberger et al., 2003; Hanessian et al., 2003; Hanessian et al., 2001; Yao et al., 2004; Venot et al., 2004).
Derivatization of specific functional groups often prevents inactivation of aminoglycosides by enzymes without compromising their antibacterial activity (Tok et al., 1999). For example, dimerization of aminoglycosides has led to better activity against resistant strains (Agnelli et al., 2004; Michael et al., 1999). Naturally occurring aminoglycosides are complex molecules, often difficult to modify chemically. The judicious protection of functional groups is critical to selective derivatization, but is time consuming ((Haddad et al., 2002; Roestamadji and Mobashery, 1998). Wong and others have developed a strategy based on the neamine scaffold and azido chemistry, to generate several neamine-based aminoglycoside analogs that have shown good antibacterial activity against resistant strains (Hanessian et al., 2003; Hanessian et al., 2001; Yao et al., 2004; Venot et al., 2004; Haddad et al., 2002; Roestamadji and Mobashery, 1998; Alper et al., 1996; Chou et al., 2004; Greenberg et al., 1999; Park et al., 1996; Ding et al., 2003; Ding et al., 2000; Verhelst et al., 2004). In spite of the recent advancements, regioselective modifications of aminoglycosides remain challenging.
A second option aimed at overcoming antibiotic resistance involves the elimination of the resistance-causing processes. Inhibiting the enzymes responsible for causing drug resistance has proven to be a valuable approach to overcome bacterial resistance. The combination of a β-lactamase inhibitor (clavulinate) and β-lactam antibiotics, has become a front line therapy for fighting β-lactam resistant bacteria (Draker and Wright, 2004; Draker et al., 2003).
Bacterial resistance to aminoglycosides occurs via mutation of the ribosome, drug efflux and most commonly via conjugation of the aminoglycoside drug by specific bacterial enzymes (Vakulenko and Mobashery, 2003; Azucena and Mobashery, 2001; Wright, 1999). The latter may arise via pathways including acetylation, adenylation or phosphorylation. These structural modifications reduce the antibiotic activity of aminoglycosides by decreasing their binding affinity for bacterial RNA.
Of the different groups of enzymes leading to aminoglycoside resistance, aminoglycoside 6′-N-acetyltransferases [AAC(6′)s] are of particular interest. This group of enzymes acts by transferring an acetyl group from acetyl coenzyme A (AcCoA) to the 6′-NH2 of a number of aminoglycosides.
In clinical isolates of aminoglycoside-resistant strains, N-acetyltransferase is the most frequently observed cause of resistance (Wright and Ladak, 1997). Examples of known AAC(6′)s include, but are not limited to AAC(6′)-Ii (Wright and Ladak, 1997), AAC(6′)-APH(2″) (Boehr et al., 2004), AAC(6′)-Ie (Culebras and Martinez, 1999), AAC(6′)-Iy (Magnet et al., 2001), AAC(6′)-29b (Magnet et al., 2003), and AAC(6′)-Iz (Li et al., 2003).
Bi-substrate analogues have been previously used for the design of inhibitors of serotonin acetyltransferase (Kim and Cole, 2001) and GCN5 histone acetyltransferase (Poux et al., 2002; Sagar et al., 2004). Williams et al. have described the gentamicin acetyltransferase I catalyzed acyl transfer to generate exclusively 3-N-chloroacetylgentamycin, which is subsequently converted to gentamicyl-3-N-acetyl CoA (Williams and Northrop, 1979).
There thus remains a need for inhibitors of aminoglycoside 6′-N-acetyltransferases. More specifically, there remains a need for inhibitors of aminoglycoside 6′-N-acetyltransferases capable of reversing or inhibiting bacterial resistance to aminoglycoside antibiotics.
The present invention seeks to meet these and other needs.
The present description refers to a number of documents, the content of which is herein incorporated by reference in their entirety.